5.6" with this one at ORD, which is biggest of this season there.
Downtown has had larger events, such as this one. However, about roughly half of the metro has not had a 6"+ storm this season.
I know not 12"+ storms, but NWS Chicago used to have a page with a list of 10"+ snowstorms. I lost the link years ago but maybe @RCNYILWXcan come up with it?